1. Field of the Invention
The present invention relates to a steering knuckle and ball joint assembly used in a tractor front axle for steering and suspension and in particular to a ball joint employing a double studded ball stud.
2. Description of Related Art
To improve tractor performance, front axle suspension systems are becoming more commonplace. A front suspension provides improved operator comfort, thereby reducing operator fatigue. In addition, the tractor frame is subject to less impact loading during operation. A front suspension axle, however, adds complexity and additional components to the front axle.
To further improve the performance of agricultural tractors, many tractors are provided with front wheel drive. While the front wheels and tires are typically smaller than the rear, by driving both the rear and the front wheels, tractive efficiency is improved. A mechanical front wheel drive requires a front drive axle with considerably more components compared to a front axle without mechanical front wheel drive.
Recent efforts to further improve tractive efficiency have focused on front axles with dual wheels on each side. While the dual front wheels improve tractive efficiency, the addition of a second wheel on each side of the front axle creates a long moment arm between the outboard tire and the turning axis about which the steering knuckle rotates for steering of the tractor. The forces applied to the steering and suspension components when the outboard tire hits an obstacle, such as a stump or bolder, is much greater than with single front tires. The ball joints of the steering system and the suspension system at the steering knuckle are critical components. To maintain the same design but with larger ball joints to accommodate the increased loads results in ball joints that are so large that the geometry of the steering and suspension systems is compromised and interferences with adjacent chassis structures result.
Accordingly, it is an object of the present invention to provide ball joints at the steering knuckle for the steering and suspension systems that provide the necessary strength for dual front wheel capability without the large size required by merely enlarging current ball joints. The ball joint of the present invention utilizes a ball stud having a spherical ball portion and a pair of studs extending oppositely therefrom for attachment to the steering knuckle. The double studded ball stud enables the overall size of the ball studs to be reduced compared to a ball stud having a single stud.
One stud of the ball stud is press fit into the steering knuckle while the other stud is captured in a cap that is secured to the knuckle by threaded fasteners. The cap clamps to the stud to securely retain the ball stud. Dowels extend through mounting apertures in the cap and into the steering knuckle to increase the shear strength of the attachment beyond that provided solely by the threaded fasteners themselves. The result is a high strength yet relatively compact ball joint design resulting in a joint that does not interfere with the packaging space required for suspension, powertrain and steering components at the front axle.
Preferably, the steering knuckle is pan shaped to surround the ball joints on all but the interior side of the knuckle where the steering and suspension arms are connected. This shielding of the ball joints protect the ball joints from dirt and debris, especially from the mud and dirt thrown by the front tires. The pan shape of the knuckle results from the knuckle having a concave inboard side creating a recess in which the ball joints are placed.